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From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: torvalds@linux-foundation.org, mingo@kernel.org,
	gregkh@linuxfoundation.org, tglx@linutronix.de, hpa@zytor.com,
	peterz@infradead.org, will.deacon@arm.com,
	linux-kernel@vger.kernel.org
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:locking/core] Documentation/atomic_t.txt: Clarify pure non-rmw usage
Date: Thu, 6 Jun 2019 10:44:21 +0200	[thread overview]
Message-ID: <20190606084421.GA5523@andrea> (raw)
In-Reply-To: <tip-fff9b6c7d26943a8eb32b58364b7ec6b9369746a@git.kernel.org>

On Mon, Jun 03, 2019 at 06:46:54AM -0700, tip-bot for Peter Zijlstra wrote:
> Commit-ID:  fff9b6c7d26943a8eb32b58364b7ec6b9369746a
> Gitweb:     https://git.kernel.org/tip/fff9b6c7d26943a8eb32b58364b7ec6b9369746a
> Author:     Peter Zijlstra <peterz@infradead.org>
> AuthorDate: Fri, 24 May 2019 13:52:31 +0200
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Mon, 3 Jun 2019 12:32:57 +0200
> 
> Documentation/atomic_t.txt: Clarify pure non-rmw usage
> 
> Clarify that pure non-RMW usage of atomic_t is pointless, there is
> nothing 'magical' about atomic_set() / atomic_read().
> 
> This is something that seems to confuse people, because I happen upon it
> semi-regularly.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Acked-by: Will Deacon <will.deacon@arm.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Link: https://lkml.kernel.org/r/20190524115231.GN2623@hirez.programming.kicks-ass.net
> Signed-off-by: Ingo Molnar <mingo@kernel.org>

I'd appreciate if you could Cc: me in future changes to this doc.
(as currently suggested by get_maintainer.pl).

This is particularly annoying when you spend time to review such
changes:

  https://lkml.kernel.org/r/20190528111558.GA9106@andrea

Thanks,
  Andrea


> ---
>  Documentation/atomic_t.txt | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> index dca3fb0554db..89eae7f6b360 100644
> --- a/Documentation/atomic_t.txt
> +++ b/Documentation/atomic_t.txt
> @@ -81,9 +81,11 @@ Non-RMW ops:
>  
>  The non-RMW ops are (typically) regular LOADs and STOREs and are canonically
>  implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and
> -smp_store_release() respectively.
> +smp_store_release() respectively. Therefore, if you find yourself only using
> +the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
> +and are doing it wrong.
>  
> -The one detail to this is that atomic_set{}() should be observable to the RMW
> +A subtle detail of atomic_set{}() is that it should be observable to the RMW
>  ops. That is:
>  
>    C atomic-set

  reply	other threads:[~2019-06-06  8:44 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-22 13:22 [PATCH 00/18] locking/atomic: atomic64 type cleanup Mark Rutland
2019-05-22 13:22 ` [PATCH 01/18] locking/atomic: crypto: nx: prepare for atomic64_read() conversion Mark Rutland
2019-06-03 13:34   ` [tip:locking/core] locking/atomic, crypto/nx: Prepare " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 02/18] locking/atomic: s390/pci: prepare " Mark Rutland
2019-06-03 13:34   ` [tip:locking/core] locking/atomic, s390/pci: Prepare " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 03/18] locking/atomic: generic: use s64 for atomic64 Mark Rutland
2019-05-22 21:16   ` Arnd Bergmann
2019-06-03 13:35   ` [tip:locking/core] locking/atomic: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 04/18] locking/atomic: alpha: use " Mark Rutland
2019-06-03 13:36   ` [tip:locking/core] locking/atomic, alpha: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 05/18] locking/atomic: arc: use " Mark Rutland
2019-05-23 23:10   ` Vineet Gupta
2019-06-03 13:36   ` [tip:locking/core] locking/atomic, arc: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 06/18] locking/atomic: arm: use " Mark Rutland
2019-06-03 13:37   ` [tip:locking/core] locking/atomic, arm: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 07/18] locking/atomic: arm64: use " Mark Rutland
2019-06-03 13:38   ` [tip:locking/core] locking/atomic, arm64: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 08/18] locking/atomic: ia64: use " Mark Rutland
2019-06-03 13:39   ` [tip:locking/core] locking/atomic, ia64: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 09/18] locking/atomic: mips: use " Mark Rutland
2019-06-03 13:39   ` [tip:locking/core] locking/atomic, mips: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 10/18] locking/atomic: powerpc: use " Mark Rutland
2019-05-23 13:27   ` Michael Ellerman
2019-06-03 13:40   ` [tip:locking/core] locking/atomic, powerpc: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 11/18] locking/atomic: riscv: fix atomic64_sub_if_positive() offset argument Mark Rutland
2019-05-22 19:06   ` Palmer Dabbelt
2019-06-03 13:41   ` [tip:locking/core] locking/atomic, riscv: Fix " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 12/18] locking/atomic: riscv: use s64 for atomic64 Mark Rutland
2019-05-22 19:06   ` Palmer Dabbelt
2019-05-23 10:23     ` Mark Rutland
2019-06-03 13:41   ` [tip:locking/core] locking/atomic, riscv: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 13/18] locking/atomic: s390: use " Mark Rutland
2019-06-03 13:42   ` [tip:locking/core] locking/atomic, s390: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 14/18] locking/atomic: sparc: use " Mark Rutland
2019-06-03 13:43   ` [tip:locking/core] locking/atomic, sparc: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 15/18] locking/atomic: x86: use " Mark Rutland
2019-06-03 13:44   ` [tip:locking/core] locking/atomic, x86: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 16/18] locking/atomic: use s64 for atomic64_t on 64-bit Mark Rutland
2019-06-03 13:44   ` [tip:locking/core] locking/atomic: Use " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 17/18] locking/atomic: crypto: nx: remove redundant casts Mark Rutland
2019-06-03 13:45   ` [tip:locking/core] locking/atomic, crypto/nx: Remove " tip-bot for Mark Rutland
2019-05-22 13:22 ` [PATCH 18/18] locking/atomic: s390/pci: remove " Mark Rutland
2019-06-03 13:46   ` [tip:locking/core] locking/atomic, s390/pci: Remove " tip-bot for Mark Rutland
2019-05-22 21:18 ` [PATCH 00/18] locking/atomic: atomic64 type cleanup Arnd Bergmann
2019-05-23 10:28   ` Mark Rutland
2019-05-23  8:30 ` Andrea Parri
2019-05-23 10:19   ` Mark Rutland
2019-05-23 11:20     ` Andrea Parri
2019-05-24 10:37     ` Peter Zijlstra
2019-05-24 11:18       ` Peter Zijlstra
2019-05-24 11:38         ` Greg KH
2019-05-24 11:42         ` Will Deacon
2019-05-24 11:52           ` Peter Zijlstra
2019-05-24 22:43             ` Andrea Parri
2019-05-28 10:47               ` Peter Zijlstra
2019-05-28 11:15                 ` Andrea Parri
2019-06-03 13:46             ` [tip:locking/core] Documentation/atomic_t.txt: Clarify pure non-rmw usage tip-bot for Peter Zijlstra
2019-06-06  8:44               ` Andrea Parri [this message]
2019-06-06  9:04                 ` Peter Zijlstra
2019-06-06  9:11                   ` Andrea Parri

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